WO 95/25626 has disclosed a method for producing a biaxially oriented plastic pipe, also known as a biaxially stretched pipe. In this method, the stretched pipe has a uniform cross section over its entire length, i.e. a uniform wall thickness and diameter, and also has a uniform draw ratio over its entire length, as seen in the axial and tangential (circumferential) directions of the pipe.
WO 97/33739 has disclosed a method for the production of a pipe from biaxially oriented thermoplastic material, which pipe has a pipe body and an integral insertion socket at one or both of its ends. This known method works on the basis of a pre-fabricated pipe made of biaxially oriented thermoplastic material, which may be formed, for example, using the method described in WO 95/25626. This pipe is then subjected to a socket-forming operation with the aid of a socket-forming device, which socket-forming device comprises a socket-forming mandrel. The socket-forming mandrel is introduced into the interior of one end part.
WO 97/10942 discloses a pre-fabricated pipe from biaxially oriented plastic material, which pipe is provided with an integral insertion socket.
Despite all the developments in the field of the production of pipes from biaxially oriented thermoplastic material, and in particular in the field of forming a socket on a pipe of this type, the socket of a pipe of this type has been found, under load tests, still to represent the critical part of the pipe. In particular, the pipe appears to yield earlier at the socket than in the pipe body, and therefore the socket undesirably restricts the load-bearing capacity of the pipe.